1. Field
This invention comprises a rapidly installed intermittent flow and storm water treatment plant employing rapid solids separation and chemical dewatering technology to produce disinfected treated recovered storm water with heavy metals removed and diluted nutrients suitable for open stream and ocean discharge.
2. State of the Art
According to Wikipedia, intermittent flows such as stormwaters are waters that originate during manmade and weather precipitation events. It may also be used to apply to water that originates with snowmelt that enters a stormwater system. Stormwater that does not soak into the ground becomes surface runoff, which either flows directly into surface waterways or is channeled into storm sewers, which eventually discharge to surface waters.
Stormwater is of concern for two main issues: one related to the volume and timing of runoff water (flood control and water supplies) and the other related to potential contaminants that the water is carrying, i.e. water pollution. Because impervious surfaces (parking lots, roads, buildings, compacted soil) do not allow rain to infiltrate into the ground, more runoff is generated than in the undeveloped condition. This additional runoff can erode watercourses (streams and rivers) as well as cause flooding after the stormwater collection system is overwhelmed by the additional flow. Because the water is flushed out of the watershed during the storm event, little infiltrates the soil, replenishes groundwater, or supplies stream base flow in dry weather.
Pollutants entering surface waters during precipitation events are termed polluted runoff. Daily human activities result in deposition of pollutants on roads, lawns, roofs, farm fields, etc. When it rains or there is irrigation, water runs off and ultimately makes its way to a river, lake, or the ocean. While there is some attenuation of these pollutants before entering the receiving waters, the quantity of human activity results in large enough quantities of pollutants to impair these receiving waters.
In addition to the pollutants carried in stormwater runoff, urban runoff is being recognized as a cause of pollution in its own right. In natural catchments (watersheds) surface runoff entering waterways is a relatively rare event, occurring only a few times each year and generally after larger storm events. Before development occurred most rainfall soaked into the ground and contributed to groundwater recharge or was recycled into the atmosphere by vegetation through evapotranspiration.
Modern drainage systems, which collect runoff from impervious surfaces (e.g., roofs and roads), ensure that water is efficiently conveyed to waterways through pipe networks, meaning that even small storm events result in increased waterway flows. In addition to delivering higher pollutants from the urban catchments, increased stormwater flow can lead to stream erosion, encourage weed invasion, and alter natural flow regimes. Native species often rely on such flow regimes for spawning, juvenile development, and migration. In some areas, especially along the U.S. coast, polluted runoff from roads and highways may be the largest source of water pollution. For example, about 75 percent of the toxic chemicals getting to Seattle, Wash. Puget Sound are carried by stormwater that runs off paved roads and driveways, rooftops, yards, and other developed land.
According to Chapter 2. Stormwater Impacts, www.waterkeeper.org/ht/a/GetDocumentAction/i/10521:
“ . . . During precipitation events or snowmelt, urban runoff takes the form of stormwater runoff—the precipitation and snowmelt that drains or runs off land surfaces and into streams and other receiving waterbodies. Under natural conditions, precipitation seeps into the ground, and filters through the soil, and recharges groundwater. Impervious surfaces are hard and rain water and melting snow cannot soak into it. As the stormwater runs over impervious surfaces like roofs, sidewalks, roads and parking lots, it picks up contaminants. Stormwater contains a deadly brew of toxic metals and chemicals, nutrients, sediments, debris, and pathogens (Natural Resources Defense Council, 2005)
While some of the stormwater universe enters our rivers and streams as non-point source pollution, much of it is either discharged through industrial or municipal storm sewer systems or from construction and other industrial facilities. According to the Clean Water Act, these discharges are point source discharges, and are subject to the Act's permitting requirements and prohibitions. Furthermore, municipal storm sewer systems often discharge pollutants even during dry weather. The Act's stormwater permitting programs include requirements for municipalities to identify and remove sources of dry weather discharges.
2.1 Water Quality, Aquatic Organisms, and Public Health
Stormwater contaminants degrade water quality and upset a waterbody's ability to maintain healthy populations of aquatic organisms. These negative impacts affect a significant proportion of Americans by contaminating drinking water sources, recreational waters, commercial fisheries, and increasing the risk of flood damage. Table 2.1.1 displays some common urban stormwater contaminants and examples of their concentrations in some stormwater.
TABLE 2.2.2Regulated stormwater constituents, comparedto freshwater acute criteria (Minton, 2005).ConstituentStormwaterCadmium (Cd)0.5-10 Chromium (Cr)10-200Copper (Cu) 5-150Iron (Fe)1000-10000Mercury (Hg)0.2-0.5 Nickel (Ni) 5-150Zinc (Zn)15-600Chlordane0.1-10 Chlorpyrifos<DL-0.10  Dieldrin0.01-0.1 Total petroleum hydrocarbons1-15pH5.5-8  Ammonia0.1-2  Nitrate0.1-1  Turbidity50-100. . .Note:all units ug/L except ammonia, nitrate, and TPH, which are mg/L and pH, which is in units.
2.1.1 Metals and Other Toxics
The contaminants found in stormwater have the potential to alter a waterbody's chemistry, exceed water quality standards, and affect both aquatic and human health. Heavy metals, including cadmium, chromium, copper, iron, manganese, nickel, lead and zinc, often originate from infrastructure like roads, guardrails, and construction materials. When precipitation lands on these and other impervious surfaces it picks up the contaminants. Stormwater also may pick up residual pesticides, petroleum products, and compounds such as polycyclic aromatic hydrocarbons (PAHs) that are also toxic to aquatic life.
Aquatic organisms are very sensitive to these toxins. Even a small amount can prove devastating. Toxic chemicals can delay or halt early development in aquatic organisms, as well as depress immune function. While sometimes only the smallest creatures are directly affected by some of these toxins, a reduction prey populations can have a ripple effect throughout the entire food web.
Toxic stormwater components also affect humans. Stormwater can pollute drinking water supplies, rendering the supply unsuitable for safe human consumption. Some contaminants like mercury, bioaccumulate and are stored in fatty tissue. A toxin enters the food chain at a low trophic level and becomes concentrated in the small organisms. As the small organisms are consumed by predators, the toxin is transferred to the ever-increasing consumers, and the pollutants move up the food chain. The amount of a bioaccumulative toxin that builds up in living tissue depends on the age of the organisms, what it eats, and where it is in the food chain. Toxins that bioaccumulate and biomagnify can affect generations of a species, and poison organisms higher in the food chain—including humans.”
The article goes on to discuss impacts of nutrients, sediments, debris, and pathogens.
Present intermittent flows such as stormwaters routinely overwhelm the capacities of a conventional wastewater treatment plant, often requiring emergency diversion basins to collect these waters until they can gradually be run through the bioreactors of a wastewater treatment plant. Unfortunately, many wastewater treatment plants do not have available space for storm collection basins. Further, storm drains often are designed to not enter conventional wastewater treatment plants and directly enter open streams or the oceans, resulting in widespread outbreaks of disease, heavy metals contamination, and suspended solids, which adversely affect wildlife and human beings.
The First Flush
Of primary importance to minimizing the effects of storm water on water quality is the FIRST FLUSH. This term describes the washing action that storm water has on accumulated pollutants in a watershed. In the early stages of runoff the land surfaces, especially the impervious surfaces like streets and parking areas, are flushed clean by the storm water. This creates a shock loading of pollutants. Studies in Florida have determined that the first one inch of runoff generally carries 90% of the pollution from a storm. Treatment of the first flush is the key to proper storm water management, and treatment of the first one inch of runoff from new development is the minimum needed to achieve the desired water quality benefits. In some cases, more than the first inch may need treatment-depending on the size of the drainage basis, the amount of impervious surface, the type of land use, the type of storm water management system and, most importantly, the type of receiving water and the desired water quality; see page 19, “Storm Water Management, A Guide for Floridians”, prepared by Eric H. Livingston, Environmental Administrator, and Ellen McCarron, Environmental Specialist, www.dep.state.fl.us/water/nonpoint/docs/nonpoint/Stormwater_Guide.pdf
Typically water quality design for sizing the First Flush is based on calculating the runoff from the first 1 to 1½ inches assuming different land infiltration characteristics; see Water Quality Design Storm: Sizing for the First Flush? By Bill Hunt, PhD, P E, Jonathan T. Smith, P E, Eban Bean, E I, NCSU Bio & Ag Engineering; www.bae.ncsu.edu/stormwater/PublicationFiles/90%.RF.DWQ.feb06.pdf. Thus, after the first flush, storm waters can often be allowed to pass without treatment as shown in FIG. 1.
There remains a need for an apparatus and method employing chemical dewatering and disinfection technology to separate and collect the solids from stormwater and provide treated disinfected and demetalized stormwater suitable for emergency release into the oceans or open streams. The device and method described below provide such an invention.